The present invention relates in general to an alkali-soluble resin having a polyaromatic group and a photosensitive composition comprising the alkali-soluble resin. More particularly, it relates to a photosensitive composition which is advantageously used for forming a color filter of color liquid crystal display devices.
Photosensitive compositions for manufacture of a color filter array include photoresists for the three primary colors—red, green and blue, and black photoresist for black matrix that surrounds color pixels for improving color contrast. Since the composition is required to have high sensitivity, adhesion to the substrate, chemical resistance and the like, a negative radiation sensitive composition is generally used.
To produce a color filter from a photosensitive composition, a black photoresist is first applied to the surface of a substrate and dried, and then exposed to radiation through a photomask and developed to dissolve unexposed portions with an alkali developer, thereby forming a pixel pattern, the so-called black matrix. These steps are repeated for the red, green, and blue photoresists, thereby completing a color filter array.
The negative photosensitive composition generally includes a pigment dispersed in a resin solution which comprises (1) an alkali-soluble resin, typically a copolymer of (a) ethylenically unsaturated monomer having a carboxyl group and (b) at least one other ethylenically unsaturated monomer, (2) a polyfunctional monomer for forming a crosslinked polymer network, (3) a photoinitiator for initiating the polymerization of the polyfunctional monomer, and (4) solvent.
Since the photosensitive composition contains a pigment dispersed in a resin solution, when a color filter is formed therefrom, the following problems arise due to poor compatibility between the pigment and the resin: (1) an undissolved product (residue or scum) of the composition may remain in unexposed portions during development; (2) mura defects may occur due to uneven distribution of the ingredients; and worse, (3) the photoresist may lose function due to aggregation of the pigment during storage.
Accordingly, the invention is generally directed to solve one or more of the above problems by providing an alkali-soluble resin having improved compatibility with the pigment.